Effects of ultrasonic-assisted germination combined with high hydrostatic pressure treatment on the quality of compound peanut-black bean sprout juice

Abstract: Bean sprouts have been a common ingredient in many Asian cuisines. The quality of bean sprouts depends mainly on the germination characteristics of bean seeds during deep processing. Thus, it is conducive to clarifying the changing rules of nutrient composition during the germination process, particularly for the high industrial-added value of germination products. This study aims to effectively improve the germination characteristics of bean seeds, and then to clarify the changes in nutrient composition during the germination process. Green deep processing was carried out for the germination products to maximumly retain the nutrients of bean sprouts. The ultrasonic treatment was first used to improve the germination rate and germination index of beans. After that, the nutrient-rich germination stage was chosen to develop the compound peanut-black bean sprout juice. A systematic investigation was made to further determine the effect of high hydrostatic pressure and conventional thermal treatment on the quality of peanut-black bean sprout juice. The results showed that the ultrasonic treatment of 300 W/10 min significantly increased the germination rate and germination index of black beans and peanuts (P<0.05). Moreover, the content of gamma-aminobutyric acid (GABA) reached 175.13 mg/100 g in the germinated black beans of the ultrasonic treatment group at the sixth germination stage (with bud length 6 cm). And the resveratrol content of peanuts in ultrasonic treatment group was 0.92 mg/g at the 5th germination stage (bud length was 2cm).At the same time, the germinated peanuts of the ultrasonic treatment group at the fifth germination stage (with bud length 2 cm) showed high content of resveratrol and GABA. Furthermore, the above-mentioned raw materials were used to prepare the compound peanut-black bean sprouts juice rich in resveratrol and GABA. The sensory and stability evaluation was carried out to optimize the formulation of compound peanut-black bean sprouts juice. The results showed that an optimal combination was achieved, when the black bean sprouts: water was 1:9 (g/mL); peanut bud: water was 1:8 (g/mL), erythritol added was 4% (w/w), black bean sprouts and peanut juice mixed ratio was 1:6; sucrose ester: single glycerol ratio was 1:1 (total amount of 0.1%), xanthan gum and cold gel added was 0.04% (w/w), and homogenization pressure was 20 MPa. The peanut-black bean sprouts compound juice presented the highest sensory score with moderate sweetness, mellow taste, and strong fragrance of buds. The best system stability was obtained in this case. Therefore, the prepared products under this condition were subjected to the subsequent thermal or high hydrostatic pressure for quality studies. Both high hydrostatic pressure (450 MPa/5 min, 450 MPa/15 min, and 450 MPa/25 min) and thermal treatment (95 °C/15 min) were selected to control the number of microorganisms within the standard. The high hydrostatic pressure pasteurization was better improved the total phenol content of compound bean sprout juice for the better color parameters of the sample, compared with the traditional thermal treatment. Moreover, the high hydrostatic pressure pasteurization (450 MPa/15 min) significantly improved the physical stability, and the total phenolic content (P<0.05). The color deterioration was also reduced in the compound peanut-black bean sprout juice. The GABA and resveratrol content were also better maintained during storage. These findings can provide the theoretical basis and technical support for the exploration of high-quality bean sprout deep-processing products. The improved storage time and added value of bean sprouts can be expected to retain the nutrients of bean sprouts during the germination process of bean seeds.